chore: update issue template to include download source

[ybw0014]

Description

We have some bug reports with the latest version from the old builds site. We may need to add one field to the checklist to mention the new builds system as well.
Although I think some people will just tick everything on the checklist without actually checking all of them, this is still something.

Proposed changes

Add a field in the checklist about the download source.

Related Issues (if applicable)

#4058, #4052, #4004

Checklist

• I have fully tested the proposed changes and promise that they will not break everything into chaos.
• I have also tested the proposed changes in combination with various popular addons and can confirm my changes do not break them.
• I have made sure that the proposed changes do not break compatibility across the supported Minecraft versions (1.16.* - 1.20.*).
• I followed the existing code standards and didn't mess up the formatting.
• I did my best to add documentation to any public classes or methods I added.
• I have added Nonnull and Nullable annotations to my methods to indicate their behaviour for null values
• I added sufficient Unit Tests to cover my code.

[github-actions]

Your Pull Request was automatically labelled as: "🧹 Chores"
Thank you for contributing to this project! ❤️

[J3fftw1]

I wonder if there is a way to make it that if you tick a box that it makes the report fail

[ybw0014]

can use actions to check issues as always.

[github-actions]

Slimefun preview build

A Slimefun preview build is available for testing!
Commit: 71da61cc

https://preview-builds.walshy.dev/download/Slimefun/4059/71da61cc

Note: This is not a supported build and is only here for the purposes of testing.
Do not run this on a live server and do not report bugs anywhere but this PR!

[JustAHuman-xD]

LGTM